Assembly for dissipating wave energy through diffraction

ABSTRACT

Blocks  20  interlock at cutouts  24  to form a row of blocks. Waves with wave crests  44  propagate in the direction of arrow A towards the blocks. When the waves impact the row of blocks  20 ,the alternating peaks and troughs formed by the edges  22 , facets and steps of blocks  20  cause reflection of the waves from a plurality of point sources such that the reflected waves have circular wave fronts  46 . The wave interference of the circular wave fronts  46  in the regions shown by reference numeral  48  results in a phenomenon known as near field diffraction. Circular wave fronts  46  also interfere with waves  44 . This reduces the wave intensity impacting the blocks.

The present invention relates to an assembly for dissipating wave energythrough diffraction, and relates particularly, but not exclusively, toan assembly for diffracting water waves.

Coastal structures such as breakwaters and seawalls are generally madefrom boulders of high density stone to create a sloping structure. Thesestructures are often overlaid with concrete shapes designed to interlockrandomly to absorb wave energy through voids.

FIG. 1 is a schematic diagram showing a known type of breakwater used atan entrance to a harbour. A plurality of large natural stone or concreteblocks 2 are sunk into the seabed 4 to form a breakwater having surfaces6 formed by blockwork 8. Blocks 2 may be cemented together. Sea waves 10propagating in the direction of arrow A impact surface 6. The waveenergy is both absorbed by the structure formed by blocks 2 and alsodirected downwardly which causes a current of water to flow in thedirection of arrow B. The horizontal planes 12 between blocks 2 act asshear planes such that the separate rows of blocks 2 can shift relativeto one another over time. Also, water forced in the direction of arrow Bcan cause an effect known as scouring which erodes the lower structureof the breakwater at the base above and below the sea level, which inextreme cases can cause the breakwater to fail and collapse.

Similar effects can also occur at structures that are used for coastaldefence, i.e. structures along a seafront rather than breakwaters.

The present invention seeks to overcome the above disadvantages of theprior art.

According to the present invention, there is provided an assembly fordissipating wave energy through diffraction, the assembly comprising:

a plurality of first blocks and a plurality of second blocks, whereineach said first and second block includes a pair of substantially planarend faces and a plurality of substantially planar side faces, wherein afirst side face meets an adjacent second side face to form an edge, andfirst and second cutouts are formed at the ends of said first and secondside faces remote from said edge, and each said first block has a firstheight between said end faces and each said second block has a secondheight, different from said first height, between said end faces;

the assembly further comprising a base row of alternating first andsecond blocks interlocked by engagement of adjacent cutouts; and

at least one further row comprising a plurality of first blocks stackedon top of the base row, at least one said further row laterally offsetfrom the base row to form a stepped assembly, each said block beinginterlocked by engagement of adjacent cutouts.

This provides the advantage that the blocks can be arranged in rowsinterlocking vertically and horizontally at adjacent cutouts, the rowsof blocks arranged such that respective edges face the incoming waterwaves to form a periodic structure that is stepped in two planes. Such aconfiguration causes wave interference from waves impacting the stepsand faces of the assembly. Each edge and face acts as a point source ofwave energy dissipation. The waves are diffracted by the faces and stepsof the assembly into the oncoming water waves to cause interference.This results in a reduced oncoming wave intensity to prolong the life ofthe structure. The wave interference creates a standing wave near theface of the structure.

By providing first and second blocks having different heights, thisprovides the advantage that the blocks can be arranged such that thestructure created is interlocked in both the horizontal and verticaldirections such that there is no horizontal shear plane as with thestructure of FIG. 1 along which the structure can slip. Also, thisprevents individual columns of blocks from falling over since the blockscan be interlocked at their respective cutouts. This provides a strongerstructure.

In a preferred embodiment, each said block comprises a bore.

This provides the advantage that the bores can be filled with concreteto further increase the strength of the structure.

Preferred embodiments of the present invention will now be described, byway of example only, and not in any limitative sense, with reference tothe accompanying drawings in which:

FIG. 1 is a cross sectional view of a breakwater;

FIG. 2 a is a plan view of a block used in forming an assembly fordissipating wave energy through diffraction;

FIG. 2 b is a front view of the block of FIG. 2 a;

FIG. 2 c is a side view of the block of FIG. 2 a;

FIG. 3 is a perspective view of a block having profiled edges;

FIGS. 4 a and 4 b are perspective views of blocks of different sizesshown in scale compared to the size of a human;

FIG. 5 is a perspective view of a block having fixtures for lifting;

FIG. 6 is a perspective view of mould parts for forming the blocks;

FIG. 7 is a perspective view of the blocks stacked in vertical columns;

FIG. 8 a is a plan view of a row of blocks interlocked to form an angledline;

FIG. 8 b is a plan view of a row of block interlocked to form a straightline;

FIG. 8 c is a plan view of a row of blocks interlocked to form a lineangled in the opposite direction to that of FIG. 8 a;

FIG. 9 is a schematic view of a row of blocks interlocked with arepresentation of the principle of diffraction;

FIGS. 10 a to 10 e are perspective and plan views showing the steps inconstruction of a vertical assembly for dissipating wave energy throughdiffraction;

FIGS. 11 a to 11 f are plan and schematic views of the steps inconstruction of a stepped assembly for dissipating wave energy throughdiffraction according to the present invention;

FIG. 12 is a cross sectional view of a stepped assembly of blocksaccording to the present invention used to protect an existing coastalprotection structure;

FIG. 13 a is a cross section of a stepped assembly of 2 metre blocks;

FIG. 13 b is a plan view of the assembly of FIG. 13 a;

FIG. 14 a is a cross section of a stepped assembly of 2.5 metre blocks;

FIG. 14 b is a plan view of the assembly of FIG. 14 a;

FIGS. 15 a to 15 d are cross sectional views showing the steps inconstruction of an assembly according to the present invention forprotecting a landslip retaining wall that has a hydraulic profile on theseaward side;

FIG. 16 is a cross sectional view of a prior art rock armour structureused to protect an existing seawall;

FIG. 17 a is a cross sectional view of a vertical assembly of blocksshown in comparison to a prior art rock armour structure; and

FIG. 17 b is a plan view of the assembly of FIG. 17 a.

Referring to FIGS. 2 a to 2 c, a block 20 is formed from concrete in acuboid shape and has forward and rear edges 22, substantially flat base23 and upper surface 25 and cutouts 24 formed at two diagonally opposedcorners. Shapes other than cuboids can be used, provided the base andupper surface are substantially flat, at least one edge and two cutoutsare formed. For example, triangular blocks can be formed by removing oneof the edges 22 of block 20. A cylindrical bore 26 is formed in thecentre of the block along the vertical axis of the block 20.

Referring to FIGS. 3 to 4 b, the edges 22 of the blocks may comprise aprofiled surface 28 to improve the appearance of the assembled blocks.FIGS. 4 a and 4 b show two different sizes of block compared to the sizeof an average man 30. An example of dimension x in FIG. 3 is of theorder of 1 metre and an example of height h in FIGS. 4 a and 4 b is 0.7and 1.1 metres respectively. It will be apparent to the person skilledin the art that the size of block can be chosen for the particularapplication.

Referring to FIG. 5, in order to lift the blocks a plurality of groves32 can be provided on the base of the blocks in order to enable liftingby machinery, such as a forklift truck. Alternatively, metal hookportions 34 can be embedded in the concrete of the block duringformation to enable lifting by a crane.

Referring to FIG. 6, each block is moulded from concrete using threereusable mould parts 36 to 40. Mould parts 36 and 38 have projections 42which are used to form the cutouts 24 in the corners of blocks 20.

Referring to FIG. 7, a plurality of blocks 20 are stacked to form twocolumns interlocked by cutouts 24. The left hand column comprises blockshaving height X and the right hand column comprises blocks having heightY. The lateral dimensions of the blocks having height X and Y are thesame such that it is only the height of the blocks that differs. It canbe seen from the drawings that as a result of the differing heights ofthe blocks, the two columns are interlocked in both the horizontal andvertical directions. For example, there is no single horizontal planethat runs across both columns. This means that there is no shear planealong which the layers of blocks can slip. Also, as a result ofinterlocking cutouts 24, the two columns are interlocked in the verticaldirection.

Referring to FIG. 8 a, a row of blocks 20 can be interlocked at cutouts24 to form an angled plane shown by angle α. Alternatively, in FIG. 8 bthe blocks are interlocked such that edges 22 present a substantiallystraight plane. Alternatively in FIG. 8 c the blocks 20 are interlockedat cutouts 24 to present a plane having angle α to the straight plane inthe opposite direction to that of FIG. 8 a.

Referring to FIG. 9, the use of a row of blocks to cause waveinterference is shown. Blocks 20 form a row of blocks on a shoreline.Waves with wave crests 44 propagate in the direction of arrow A towardsthe shore. When the waves impact the row of blocks 20, the alternatingpeaks and troughs formed by the edges 22 of blocks 20 cause deflectionof the waves from the faces of the assembly such that the deflectedwaves have circular wave fronts 46. The wave interference of thecircular wave fronts 46 in the regions shown by reference numeral 48results in a phenomenon known as near field diffraction. Circular wavefronts 46 also interfere with incoming waves 44.

The reflected wave crests from adjacent blocks cause diffraction. Thiswave pattern interferes with inbound waves 44 and as a result theincident wave spectrum is modified and becomes less coherent. Thiscauses a wave calming effect on the surface of the water, which iswitnessed as choppy water and results in the peak wave height beingreduced when the modified waves impact the structure. As a result of thereduction of the wave amplitude impacting the structure, the wave energyis reduced which leads to a reduced scouring effect.

Two node lengths N_(o) and N₁ are shown in FIG. 9. Node length N_(o) isformed by two adjacent edges 22 whereas node length N₁ is formed as aresult of the contour of five interlocking blocks. It will beappreciated by persons skilled in the art that the node length can bechosen to cause wave reflection suitable for diffracting incoming wavesof different wavelengths.

Referring to FIGS. 10 a to 10 e, construction of a generally verticalstructure for reflecting water waves will be described.

FIGS. 10 a and 10 b show a first row of blocks having two blocks 20 a ofheight Y interlocked with a central block 20 b of height X. FIG. 10 ashows a base row of three blocks. However, any amount of blocks can beused to form a row of required size provided that blocks havingalternating height X and Y are used to form a stepped base layer.Referring to FIGS. 10 c and 10 d, a further layer of blocks 20 b havingheight X are placed on the base blocks 20 a having height Y.

Referring to FIG. 10 d, block 20 b having height X (such that all of theblocks in the second row have height X) is placed on the base block 20 ahaving height X. It can be seen from FIG. 10 d that two horizontalplanes 50 and 52 are formed between the base row and the second row.This means that there is no shear plane along which the second row canslip when subjected to wave impact. The interlocking of blocks atcutouts 24 also provides a vertical interlock. In FIG. 10 e, furtherblocks 20 b having height X are placed on the second row to form a thirdrow. In the vertical column assembly of FIGS. 10 a to 10 e, the bores 26of each block are vertically aligned. The bores can be filled withconcrete and/or piled to increase the strength of the structure.

The vertical structure of FIGS. 10 a to 10 e is suitable for use as abreakwater, i.e. a generally vertical structure that is used as a pierfor an entrance to a harbour. It should be understood that blocks 20 aand 20 b can be used to form only the water facing surfaces of thestructure, and other materials can be used behind the blocks.

Referring to FIGS. 11 a to 11 f, construction of a stepped assembly forreflecting water waves will now be described.

Referring to FIGS. 11 a and 11 b, a base row of blocks 20 a havingheight Y and blocks 20 b having height X is formed, the blocksinterlocking at cutouts 24.

Referring to FIGS. 11 c and 11 d, blocks 20 b in a second row are placedon blocks 20 a of the first row. Blocks 20 b in the second row arerearwardly displaced from blocks 20 a of the first row. However, cutouts24 of the second row of blocks still interlock with cutouts 24 of blocks20 b in the first row as shown in FIG. 11 d.

Referring to FIG. 11 e, the completed second row comprises blocks 20 ball having height X. As a result of blocks 20 a having height Y in thefirst row, the first and second rows are interlocked in two horizontalplanes 50 and 52. Also, by laterally offsetting the second rowrearwardly from the first row a stepped configuration is formed. Itshould be noted that even with the stepped configuration the blocks allinterlock in both the horizontal and vertical directions. Such a steppedconfiguration is useful for coastal defence assemblies.

Referring to FIG. 12, an assembly of blocks 20 can be used to protect anexisting seawall 54. A base block 20 c is placed on a bed 56 adjacent tothe sea 58. The blocks are then stacked in the configuration shown inFIGS. 11 a to 11 f. The region behind the blocks 20 can be filled withrecycled concrete, earth or lean mix 60.

FIGS. 13 a to 14 b show different configurations of blocks 20 havingdifferent sizes. It will be apparent to the skilled person that blocksof different sizes can be chosen to satisfy different structural andtidal conditions.

Referring to FIGS. 15 a to 15 d, the same principle as FIGS. 12 to 14can be used to protect a landslip 62. A base block 20 c is placed on abeach 64 and the region between the landslip 62 and the blocks 20 isfilled with concrete or lean mix 60. It should also be noted that thecylindrical bores 26 can be filled with concrete even in the steppedconfiguration in order to reinforce the structure.

Referring to FIG. 16, a prior art method of reinforcing an existingseawall 54 is shown. A rock armour barrier 64 is formed from rocks 66stacked on the seabed 68. Referring to FIGS. 17 a and 17 b, the sameseawall 54 can be protected by stacking blocks 20 in the verticalconfiguration of FIGS. 10 a to 10 e. It can be seen from the drawingsthat the lateral extent of the assembly of blocks 20 of FIG. 17 a ismuch less than the lateral extent of the existing rock armour barrier64. This means that less material is required.

It will be appreciated by person skilled in the art that the aboveembodiments have been described by way of example only, and not in anylimitative sense, and that various alternations and modifications arepossible without departure from the scope of the invention as defined bythe appended claims.

1. An assembly for dissipating wave energy through diffraction, theassembly comprising: a plurality of first blocks and a plurality ofsecond blocks, wherein each said first and second block includes a pairof substantially planar end faces and a plurality of substantiallyplanar side faces, wherein a first side face meets an adjacent secondside face to form an edge, and first and second cutouts are formed atthe ends of said first and second side faces remote from said edge, andeach said first block has a first height between said end faces and eachsaid second block has a second height, different from said first height,between said end faces; the assembly further comprising a base row ofalternating first and second blocks interlocked by engagement ofadjacent cutouts; and at least one further row comprising a plurality offirst blocks stacked on top of the base row, at least one said furtherrow laterally offset from the base row to form a stepped assembly, eachsaid block being interlocked by engagement of adjacent cutouts.
 2. Anassembly according to claim 1, wherein each said block comprises a bore.